Heat shrink tunnel for ensuring uniform shrinkage of heat shrinkable bands on articles of various sizes

ABSTRACT

A heat shrink tunnel for shrinking heat shrinkable articles disposed on a conveyor including a pair of elongated bilateral heat ducts each of which is disposed on a respective side of said conveyor. Each duct includes a vent extending substantially the entire length thereof. Means are provided to force air into the ducts and through their associated vents to contact the articles on the conveyor as the articles move downstream. The ducts are supported by adjustable means and are oriented such that each extends upwards away and converges laterally towards the conveyor in the downstream direction.

United States Patent 1 1 11 1 02 Laessig May 7, 1974 [54] HEAT SHRINK TUNNEL FOR ENSURING 3,281,958 11/1966 Lambert et a]. 34/225 UNIFORM SHRINK AGE OF HEAT 2,851,763 9/1958 Adams SHRINKABLE BANDS ON ARTICLES OF VARIOUS SIZES Primary ExaminerKenneth W. Sprague Assistant Examiner-James C. Yeung [75] Inventor: John Laessig Newtown Square Attorney, Agent, or Firm-Caesar, Rivise, Bernstein & [73] Assignee: Gilbreth Company, Philadelphia, Co n [22] Filed: Mar. 15, 1973 [57] ABSTRACT [21] Appl. No.: 341,412 A heat shrink tunnel for shrinking heat shrinkable articles disposed on a conveyor including a pair of elon- [52] U S Cl 34/218 34/105 34/229 gated bilateral heat ducts each of which is disposed on "34/236 33/184 219/388 a respective side of said conveyor. Each duct includes [51] Int Cl F26b 19/00 a vent extending substantially the entire length [58] Fie'ld 222 230 thereof. Means are provided to force air into the ducts 34/232 208 53/30 and through their associated vents to contact the arti- 5 5 5 432/175 cles on the conveyor as the articles move downstream. The ducts are supported by adjustable means and are 1561 2251;363:2112tzazfidzitsiztszfiz 1:10:11

UNITED STATES PATENTS Stream direction 3,312,811 4/1967 Shanklin 34/225 3,389,478 6/1968 Cline 34/225 16 Claims, 6 Drawing Figures 54 7 2o 76 54 s 100 38 102 98 86 9s 94 74 W 4e 92 82 24 22 84 D 8 92 90 5o 36 9O 80 A20 I2 56 l 6O PATENTEUIAY 1 m4 3308.702 sum 1 or 2 WEE;- 24 I j a!) T I J FIG. 2 28 I08 I08 :08 FIG. 3a 06 FIG. 3c

I06 I04 I I04 I04 PATENTEMY 1:914 3.808.702

SHEET 2 OF 2 heat shrinkable articles of various sizes.

It is known to provide a heat shrink tunnel wherein hot air is forced into an enclosure through which articles including heat shrinkable plastic materials pass. In subjecting such articles to heat shrink techniques, it is often desirable that the articles first be subjected to a warm zone of air and then be subjected to a hot zone of air so that the articles are first subjected to a warming action which is followed by a hot heating action in order to fully activate or shrink the heat shrink plastic. This presents a problem since the hotter zone is located downstream of the warm zone.

Prior to co-pending US. Pat. application Ser. No. 92,623 filed on Nov. 25, 1970 now US. Pat. No. 3,711,961, which is assigned to the same assignee as this invention, it had been suggested that hot air simply be forced upstream in a direction against the normal downstream movement of the conveyor. However, it has been found that the downstream movement of the conveyor creates considerable resistence to upstream movement of hot air, and thus efforts to achieve a warm zone at an upstream point have been largely ineffective.

In said co-pending United States patent application, there is disclosed a relatively simple heat shrink tunnel for producing an upstream warming zone and a downstream hot heat zone. That tunnel comprises an enclosure, a conveyor to conduct articles through the enclosure from an upstream point to a downstream point, conduit means to deliver hot air to the enclosure, and partition means to divide the conduit means into first and second paths. The first path is relatively long as compared to the second path. The tunnel also includes a source of hot air and means to force the hot air in a generally upstream direction in the two paths of the conduit means. A first slit is provided in the conduit means in an upstream point communicating with the enclosure to allow hot air in the first path to enter the enclosure in a narrow band. A second slit is provided in the conduit means spaced downstream of the first slit and also communicating with the enclosure to allow hot air to enter the enclosure in a narrow band at a point that is downstream from the first slit whereby the air entering through the second slit and at the downstream location is relatively hot.

ln co-pending US. Pat. application Ser. No. 11,762, filed on Mar. 12, 1970 now US. Pat. No. 3,640,417 and assigned to the same assignee as this invention, there is disclosed a closure for acontainer which permits, when on: display, a customer to look into and smell the-product packaged therein but, nevertheless, prohibits the customer from touching it directly. The container is sealed at its mouth portion by a flat, porous top member and has provided at the outer periphery of the container a U-shaped tongue for use in removing the entire closure when the container is to be opened. The closure comprises a heat shrinkable cylindrical portion and a non-heat shrinkable cylindrical portion, the latter being secured to a non-heat shrink able end portion to form a cup. In this way, there is minimum shrinkage axially and maximum shrinkage diametrically when heat is applied.

As disclosed in the first aforementioned patent application, in order to lock the heat shrinkable cylindrical portion at its bottom to the container and to prevent the upward movement of the cylindrical portion during the remainder of the heat shrink process, the conveyor can be oriented to move along an upward incline with respect to the tunnel in the downstream direction. Furthermore, the heat shrink tunnel as disclosed therein is particularly suited for use in shrinking heat shrinkable bands around containers of a broad range of sizes.

It is a general object of this invention to provide a novel apparatus for uniformly shrinking heat shrinkable means on articles of various sizes.

It is a further object of this invention to provide a heat shrinkage apparatus which permits the most ideal heat flow pattern to be directed at a container of a given size and shape moving through the apparatus.-

It is yet a further object of this invention to provide a novel heat shrink tunnel including fully adjustable duct configurations to permit the most ideal heat flow pattern to be directed at a container of a given size and shape moving through the tunnel.

It is still a further object of this invention to provide a novel heat shrink tunnel for use with any existing conveyor for uniformly shrinking heat shrinkable means on articles moved by the conveyor.

It is yet a further object of this invention to provide a novel shrink tunnel in which the path through which the articles move is opened and clearly visible at all times.

It is yet another object of this invention to provide in a novel heat shrink tunnel including bilateral heating ducts so constructed that their exposed outer surfaces remain cool in interests of personnel safety.

The foregoing as well as other objects of this invention are achieved by providing in combination with a conveyor to conduct articles from an upstream point to a downstream point, an improved heat shrink tunnel disposed adjacent to the conveyor between the points. The tunnel comprises a first elongated heat duct in cluding an elongated vent extending substantially the entire length of the duct, support means for supporting the duct on one side of the conveyor and at a horizontal and vertical angle with respect thereto and means to force hot air through the duct and through the elongated vent in the duct to contact the articles as they move along the conveyor in the downstream direction. The tunnel also comprises a second elongated heat duct constructed similar to the first elongated heat duct and oriented in the same manner. Both heat ducts are adjustably mounted and are oriented such that each extends upward away and converges laterally towards the conveyor in the downstream direction. The ducts each include a plenum chamber into which cool air is brought. The air exiting the chamber passes over heaters which are separated from the plenumchamber by an insulating wall, the resulting heated airexits the duct via its vent.

Other objects and many of the attendant advantages of the invention will become readily apparent by reference to the drawings wherein:

FIG. 1 is a perspective view showing a heat shrink tunnel embodying the present invention;

FIG. 2 is a section view taken along line 22 of FIG.

FIG. 3A is a schematic diagram of the orientation of the ducts shown in FIG. 1;

FIG. 3B is a schematic diagram of a variant duct orientation;

FIG. 3C is a schematic diagram of another variant duct orientation.

FIG. 4 is an enlarged sectional view taken along line 44 of FIG. 1.

Referring now in-greater detail to the various figures of the drawing wherein like reference characters refer to like parts, there is shown at 20 in FIG. 1 a heat shrink tunnel embodying the present invention.

The heat shrink tunnel 20 basically comprises a pair of bilateral heating ducts 22 and 24 disposed on oppo site sides of a conveyor 26 which moves in the direction of arrow 28 from an upstream point 30 (FIG. 3A) to a downstream point 32 (FIG. 3A). The conveyor 26 forms no part of the heat shrink tunnel but merely serves as a means for supporting and moving a plurality of articles through the tunnel at a predetermined rate in order to heat-treat a portion of said articles. Conduit means 34 and 36 are provided in order to deliver air to the interior of heating ducts 22 and 24, respectively, from respective electrical blowers 38 and 40. Electrical heaters are provided within the heating ducts and serve to heat the incoming air to a high'temperature, e.g., 400 F. Electrical power is provided to the blowers 38 and 40 via cables 42 and 44, respectively, from an electrical control box 46. Adjustable support means 48 is provided to support the heating ducts in an orientation for best effectuating the expeditious heating of heat shrinkable means on the articles moved by the conveyor 26.

Each of the bilateral heat ducts 22 and 24 is of elongated rectangular shape and includes an inner-face. A slot or vent is provided in the lower portion of the inner-face of each duct and extends substantially the entire length of the duct parallel to the base thereof. In FIG. 1 only vent, 50, in the lower portion of the innerface 52 of the heating duct 22 can be seen. A similar vent is provided in the lower portion of the inner-face of duct 24 extending along the length thereof and parallel to the base.

The electrical blower 38 is mounted, by suitable means (not shown) on heating duct 22 and electrical blower 40 is mounted by suitable means (not shown) on duct 24.

Each of the electrical blowers 38 and 40 are adapted, when energized, for drawing in ambient air and forcing it through an associated conduit into the associated heater duct. To that end, conduit means 34 is connected between the blower 38 and heating duct 22. A I

similar conduit 36 is connected between the blower 40 and its associated heating duct 24. The physical connection between the conduit and the associated heating duct and blower is effectuated via conventional connecting means.

Electrical power is provided to the blowers 38 and 40 via electrical cables 42-and 44, respectively, from the control box 46. The cables are relatively flexible in order not to impede the adjustment of the orientation of the heating ducts as may be required.

In accordance with one aspect of this invention, the ducts are adapted for adjustment in the horizontal as well as vertical directions.

As can be seen in FIG. I, support means 48 include four vertically oriented legs 54. Each leg is of rectangular cross section and includes at its lower end a flanged portion 56 which forms a foot piece for resting upon a surface adjacent the conveyor 26. Each foot piece includes a hole 58 therein through which a threaded fastener such as a screw 60 may be disposed to secure the leg to the surface adjacent the conveyor. I

As can be seen in FIG. 1, two of the legs 54 are dis posed on one side of the conveyor 26 and the remaining two legs 54 are disposed on the opposite side of the conveyor. A pair of side bars 62 are provided to connect the upper ends of the pairs of legs on opposite sides of the conveyor. For example, one side bar 62 connects the upper end of the pair of legs on the near side of the conveyor 26 and another side bar 62 connects the upper portion of the pair of legs disposed on the opposed side of the conveyor. A pair of bridging bars 64 are provided between opposed legs 54. The bridging bars, side bars and legs are connected together via a plurality of threaded fastening means or screws (not shown).

As will be appreciated when viewed down the conveyor, the legs 54, side bars 62, bridging bars 64 and ducts 22 and 24 form an open tunnel-like configuration straddling the conveyor.

In order to achieve the most ideal heat flow pattern to an article moving on the conveyor 26 through the tunnel 20, the heating ducts are adapted for lateral and vertical adjustment. To that end, a hole 66 is provided in each of the bridging members 64 at approximately the middle thereof. A threaded shaft 67 passes through the hole in the bridging member 64 adjacent the downstream end of the tunnel 20 and a similar threaded shaft 68 passes through the hole in the middle of the bridging member 64 adjacent the upstream end of the tunnel. A handwheel 70 is threadedly engaged on shaft 67 and abuts the top surface of the bridging member 64 adjacent the downstream end of the tunnel and a similar handwheel 72 is threadedly engaged on shaft 68 and abuts the top surface of bridging member 64 adjacent the upstream end of the tunnel. Each of the handwheels is. adapted for raising or lowering the associated threaded shaft.

As can be seen, the lower end of each of the shafts 67 and 68 includes a holding member 74 and 76, respectively. Member 74 includes a hole 78 therein through which a support shaft 80 passes. Support shaft 80 is centered through member 74 and is held in place via a set screw 82. In a similar manner, support member 76 includes a hole 84 therein through which hole support shaft 86 passes. Shaft 86 is held in place within support 76 via set screw 88. A yoke member 90 is connected on the top face of each of the ducts adjacent their downstream end. Each yoke includes a pair of upstanding ears 92 each having an elongated slot 94 therein. A pair of yoke members 96 are connected on the respective top faces of each of the ducts 22 and 24 adjacent their upstream end. Each yoke includes a pair of upstanding ears 98 each having an elongated slot 100 therein. Slots 94 and 100 are elongated and are arranged in a generally horizontal orientation in order to enable lateral adjustment of the ducts as will be described in detail later.

As can be seen in FIG. 1, the support shaft passes through slots 94 in yokes 90 and thereby serves to support the downstream ends of the ducts 22 and 24 and the support shaft 86 passes through the slots 100 in yoke 96 to support the upstream ends of the duct.

The vertical orientation of the ducts 22 and 24 can be adjusted by rotating handwheel 70. This action causes the shaft 67 to move vertically, upwards or downwards depending upon the direction that the handwheel is rotated, thereby carrying support member 74, support shaft 80, yokes 90 and the downstream ends of ducts 22 and 24 to the desired vertical orientation.

As should be appreciated, the downstream end of the ducts can be raised to a higher elevation with respect to the conveyor than the upstream ends by rotating handwheel 70, such that threaded shaft 66 moves upward, while leaving handwheel 72 in position. A threaded thumb nut 102 is provided on threaded shaft 67 adjacent the underside of bridging bar 64. Once the position of the downstream ends of the heating ducts 22 and 24 have been adjusted by the rotation of handwheel 70, thumb nut 102 is rotated to firmly abut the contiguous surface of bridging member 64 thereby locking the threaded shaft in its vertical position.

The upstream end of the heating ducts 22 and 24 can also be raised or lowered in a similar manner and once moved into that position can be locked in place by rotating thumb nut 102 which is disposed on threaded shaft 68 adjacent the underside of the upstream bridging bar 64.

As previously mentioned, each of the heating ducts 22 and 24 may be adjusted laterally with respect to the conveyor 26. Such adjustment is effectuated by sliding the end of the duct to be adjusted via its associated supporting yoke along the associated support shaft. For example, if it is desired that the upstream ends of the ducts be separated by a greater distance than the downstream ends of the ducts, i.e., the upstream ends of the ducts be spaced a greater distance laterally of the conveyor than the downstream ends of the ducts, the upstream ends of the ducts, may be pivoted outward laterally by sliding their associated yokes 96 outwards and away from holding member 76 and/or the downstream ends of the ducts may be pivoted laterally by sliding their associated yokes inwards and towards holding member 74.

In view of the fact that heat tunnel 20 is arranged such that its bilateral heating ducts 22 and 24 can be adjusted for various orientations, the most ideal heat flow pattern can be directed at an article of a given size .and shape on the conveyor. For example, in order to best shrink heat shrinkable bands about containers, the heat shrink tunnel can be arranged as follows: The height of the duct with respect to the conveyor is first established by rotating the associated handwheels such that the downstream ends of the duct are at an elevation at which their vents are slightly below the lower edge of the band of heat shrinkable material on the container and the upstream ends of the ducts are at an elevation at which their vents are approximately even with the upper edge of the bands. The ducts are locked in this position by tightening thumb nuts 102.

The heat shrink tunnel shown in FIG. 1 is oriented in such a manner.

As can be seen in the partial sectional view of FIG. 2, a plurality of containers or bottles 104, 106, 108 and 110 are disposed on conveyor 26. Each bottle includes a heat shrinkable tube 112, 114, 116 and 118, respectively, disposed about its neck. As can be seen, the heat shrinkable tubes are in varying states of shrinkage de- 6 pending upon their position within the heat shrink tunnel 20.

Upon a bottle entering the tunnel, such a bottle being exemplified by bottle 104, the stream of hot air exiting vent 50 in duct 22 and the opposed vent in duct 24 begins to heat the heat shrinkable band 112 at the lower edge thereof. As the bottle moves down the conveyor 26, in the direction of arrow 28, the stream of air moves upward with respect to the band due to the fact that the ducts 22 and 24 are angled upward with respect to the conveyor in the downstream direction and thus the lower portion of the band begins to shrink about the bottle. This condition is shown by band 114 on bottle 106. As the bottle moves further downstream, the stream of air from the ducts moves further up the band, thus causing more of the band to shrink about the bottles neck. This condition is shown by band 116 on bottle 108. As the bottle reaches the end of the tunnel, the stream of air is approximately level with the top of the band, thereby completing the shrinkage of the entire band. This condition is shown by band 118 on bottle 1 10.

As will be appreciated by those skilled in the art, the orientation of the ducts is described causes the expeditious shrinkage of the band about the bottle in that the band is initially tightly secured by its bottom portion to the bottle as the bottle begins passage through the tunnel. This action precludes the band from riding up during the subsequent heating. Furthermore, by orienting the ducts so that they are angled upward with respect to the conveyor in the downstream direction, and with the upstream end of the ducts just slightly below the bottle, the heating of the contents of the bottle is minimized.

In FIG. 3 there is shown, via three schematic diagrams, 3A, 3B and 3C, of three possible lateral orientations of the heating ducts 22 and 24 with respect to the conveyor. As can be seen in FIG. 3A, the ducts are oriented such that they converge laterally toward the conveyor in the downstream direction.

The duct orientation shown schematically in FIG. 3A is the orientation of the ducts 22 and 24 shown in FIG. 1. As should be appreciated, with such a duct orientation the temperature of the air contacting the upstream bottles will be cooler than that contacting the downstream bottles due to the closer proximity of the ducts to the bottles at the downstream ends of the tunnel. Accordingly, the duct orientation shown in FIGS. 1 and 3A provide an upstream warm zone and a downstream hot zone within the tunnel.

In FIG. 3B there is shown the condition wherein the ducts are oriented laterally parallel to one another.

In FIG. 3B there is shown the condition wherein the ducts are oriented with the downstream ends divering laterally away from the conveyor in the downstream direction. I

In FIG. 4 there is shown the construction of bilateral heating duct 24. Bilateral heating duct 22 is constructed in an identical manner as duct 24.

As can be seen, bilateral duct 22 includes a top wall or face 120, a back wall or face 122, a bottom wall or face 124 and a front wall or face 126 in which air vent 50 is provided. The duct also includes a pair of end walls 128 (see FIG. 2).

An air inlet port 130 is provided in the backwall 122 and is connected to conduit 36 by conventional coupling means (not shown).

A thermally insulating wall 132 is disposed within duct perpendicular to topwall 122 and extends the entire length thereof. The insulating wall 132 is connected to topwall 122 by suitable means (not shown) and defines a plenum chamber 134 between itself and walls 120, 122 and 124.

As can be seen, wall 132 extends almost to the bottom wall 124, the space between the lower edge of wall 132 and bottom wall 124 defining a vent 136 from which air can exit the plenum chamber 134.

The frontwall 126 of duct 24 is also formed of a thermally insulating material.

The space within duct 24 between walls 132 and 126 serves as a heating chamber 138. The wall 132 serves to thermally insulate the plenum chamber 132 from the heating chamber 138.

As can be seen, three ribbon-element, electrical heaters 140, 142 and 144 are stacked on top of the other within chamber 138. Each heater includes a plurality of heat radiating fins 146. A thermal barrier 148 is provided between heaters 140 and 142 and between heaters 142 and 144. Heater 140 is mounted on a thermally insulating support 150 on bottomwall 124. The combination of the heaters and interposed barriers forms a vertical heating wall over which air exiting the vent 136 in plenum chamber 134 passes in route to exit vent 50 of the duct.

Due to the fact that the wall 132 insulates chamber 134 from chamber 138, the cool air forced into the plenum chamber by the associated blower is not heated significantly. Accordingly, the duct wall portions forming the plenum chamber remain relatively cool. Since the wall portions forming the plenum chamber are the outside portions of the tunnel, i.e., the portions personnel are most likely to come into contact with, the danger of operating personnel sustaining a burn if accidental contact is made to the heating duct is greatly diminished.

The incoming air is heated in the following manner: cool air is forced through port 130 by blower 136, the air warms slightly in the plenum chamber and exits through vent 136 into heating chamber 138. Once in the heating chamber, the air flows up the heater wall across the back faces of the heaters 140, 142 and 144, i.e., the faces closest to the wall 132, in the direction of the arrows whereupon the air is progressively heated. The air then flows in the direction of the arrows down the heater wall across the front faces of heaters 144, 142 and 140.

By the time the air reaches exit vent 50, it has been progressively heated to approximately 400 F. by'all of the faces of all of the heaters. Vent 50 serves as the outlet vent of the heating chamber so as to enable hot air produced therein to contact the articles on the moving conveyor 26. The insulation support 150 serves to prevent the transfer of heat from the hot exiting air to the bottomwall 124.

By mounting the heaters to form a heating wall, each heater in the wall is exposed to approximately the same thermal environment. For example, heater 140 is exposed to cool air on its side facing wall 132 and hot air on its other side. This has the same thermal effect on the heater as the moderatly hot air to which both sides of heater 144 are exposed. This action increases heating efficiency.

In view of all of the foregoing, it should be appreciated that the heat shrink tunnel 20 of this invention can be readily adapted for shrinking a wide variety of sizes and shapes of banded articles by the simple orientation adjustment of its bilateral heating ducts. Furthermore, the open nature of the tunnel 20 enables the conveyor and articles thereon within the tunnel to be readily viewed during operation, thereby enabling corrective measures to be taken in the event of misoperation. Further still, the internal construction of the heating ducts ensures the efficient production of high temperature air while its exposed surface are kept cool in the interests of personnel safety.

Without further elaboration, the foregoing will so fully illustrate my invention, that others may, by applying current or future knowledge, readily adapt the same for use under various conditions of service.

What is claimed as the invention is:

1. In combination with a conveyor to conduct articles from an upstream point toa downstream point, an improved heat shrink tunnel disposed adjacent said conveyor between said points, said tunnel comprising a first elongated heat duct including an elongated vent extending substantially the entire length of said duct, support means for supporting said duct on one side of said conveyor and at a horizontal and vertical acute angle with respect thereto and means to force hot air through said duct and through said elongated vent to contact said articles as they move along the conveyor in the downstream direction, such that when said duct is at an upward acute vertical angle in the downstream direction, the point of contact of the hot air on the article moves up the article as the article moves along the conveyor and when said duct is at a downward acute vertical angle in the downstream direction, the said point of contact moves down the article as the article moves along the conveyor.

2. The combination as specified in claim 1 wherein said duct extends at an upward acute angle with respect to said conveyor in the downstream direction.

3. The combination as specified in claim 2 wherein said support means is vertically adjustable such that the degree of said upward angle can be established as desired.

4. The combination as specified in claim 1 wherein said duct extends at a lateral acute angle with respect to said conveyor in the downstream direction.

5. The combination as specified in claim 4'wherein said support means is horizontally adjustable such that the degree of the lateral angle can be established as desired.

6. The combination as specified in claim 5 wherein said duct extends at an upward acute angle with respect to said conveyor in the downstream direction.

7. The combination as specified in claim 6 wherein said support means is vertically adjustable such that the degree of said upward angle can be established as desired.

8. The combination as specified in claim 1 wherein said tunnel also comprises a second elongated heat duct supported by said support means on the opposed side of said conveyor and at a horizontal and a vertical acute angle with respect thereto, said second elongated heat duct including an elongated vent extending substantially the entire length of said duct, and means to force hot air through said duct and through said elongated vent to contact said articles as they move long the conveyor in the downstream direction, such that when said duct is at an upward acute vertical angle in the 10. The combination as specified in claim 9 wherein said support means is vertically adjustable such that the degree of said upward angle can be established as desired.

11. The combination as specified in claim 10 wherein said second duct extends at a lateral acute angle with respect to said conveyor in the downstream direction.

12. The combination as specified in claim 11 wherein said support means is horizontally adjustable such that the degree of said lateral angle can be established as desired.

13. In combination with a conveyor to conduct articles from an upstream point to a downstream point, an improved heat shrink tunnel disposed adjacent said conveyor between said points, said tunnel comprising a first elongated heat duct including a front wall having an elongated vent extending substantially the entire length thereof, a rear wall disposed on the opposite side of the duct from the front wall and support means for supporting said duct on one side of said conveyor, with the front wall disposed immediately adjacent the conveyor, said heat duct being adapted for directing a stream of hot air at the side of said articles and including a plenum chamber immediately adjacent said rear wall for receiving relatively cool air therein and a heating chamber immediately adjacent the front wall for heating the air from the plenum chamber and thermally insulating means disposed between said chambers such that said plenum chamber remains relatively cool, said elongated vent serving as the outlet for said heating chamber.

14. The heating duct as specified in claim 13 wherein a plurality of electrical heaters are provided within said heating chamber.

15. The heating duct as specified in claim 14 wherein said heaters are stacked one upon another to form a heating wall over which air from said plenum chamber flows.

16. The heating duct as specified in claim 15 wherein the wall is vertical and wherein the air flows up one face thereof and down the other face thereof and exits through said elongated vent. 

1. In combination with a conveyor to conduct articles from an upstream point to a downstream point, an improved heat shrink tunnel disposed adjacent said conveyor between said points, said tunnel comprising a first elongated heat duct including an elongated vent extending substantially the entire length of said duct, support means for supporting said duct on one side of said conveyor and at a horizontal and vertical acute angle with respect thereto and means to force hot air through said duct and through said elongated vent to contact said articles as they move along the conveyor in the downstream direction, such that when said duct is at an upward acute vertical angle in the downstream direction, the point of contact of the hot air on the article moves up the article as the article moves along the conveyor and when said duct is at a downward acute vertical angle in the downstream direction, the said point of contact moves down the article as the article moves along the conveyor.
 2. The combination as specified in claim 1 wherein said duct extends at an upward acute angle with respect to said conveyor in the downstream direction.
 3. The combination as specified in claim 2 wherein said support means is vertically adjustable such that the degree of said upward angle can be established as desired.
 4. The combination as specified in claim 1 wherein said duct extends at a lateral acute angle with respect to said conveyor in the downstream direction.
 5. The combination as specified in claim 4 wherein said support means is horizontally adjustable such that the degree of the lateral angle can be established as desired.
 6. The combination as specified in claim 5 wherein said duct extends at an upward acute angle with respect to said conveyor in the downstream direction.
 7. The combination as specified in claim 6 wherein said support means is vertically adjustable such that the degree of said upward angle can be established as desired.
 8. The combination as specified in claim 1 wherein said tunnel also comprises a second elongated heat duct supported by said support means on the opposed side of said conveyor and at a horizontal and a vertical acute angle with respect thereto, said second elongaTed heat duct including an elongated vent extending substantially the entire length of said duct, and means to force hot air through said duct and through said elongated vent to contact said articles as they move long the conveyor in the downstream direction, such that when said duct is at an upward acute vertical angle in the downstream direction the point of contact of the hot air on the article moves up the article as the article moves along the conveyor and such that when said duct is at a downward acute vertical angle in the downstream direction the said point of contact moves down the article as the article moves along the conveyor.
 9. The combination as specified in claim 8 wherein said second duct extends at an upward acute angle with respect to said conveyor in the downstream direction.
 10. The combination as specified in claim 9 wherein said support means is vertically adjustable such that the degree of said upward angle can be established as desired.
 11. The combination as specified in claim 10 wherein said second duct extends at a lateral acute angle with respect to said conveyor in the downstream direction.
 12. The combination as specified in claim 11 wherein said support means is horizontally adjustable such that the degree of said lateral angle can be established as desired.
 13. In combination with a conveyor to conduct articles from an upstream point to a downstream point, an improved heat shrink tunnel disposed adjacent said conveyor between said points, said tunnel comprising a first elongated heat duct including a front wall having an elongated vent extending substantially the entire length thereof, a rear wall disposed on the opposite side of the duct from the front wall and support means for supporting said duct on one side of said conveyor, with the front wall disposed immediately adjacent the conveyor, said heat duct being adapted for directing a stream of hot air at the side of said articles and including a plenum chamber immediately adjacent said rear wall for receiving relatively cool air therein and a heating chamber immediately adjacent the front wall for heating the air from the plenum chamber and thermally insulating means disposed between said chambers such that said plenum chamber remains relatively cool, said elongated vent serving as the outlet for said heating chamber.
 14. The heating duct as specified in claim 13 wherein a plurality of electrical heaters are provided within said heating chamber.
 15. The heating duct as specified in claim 14 wherein said heaters are stacked one upon another to form a heating wall over which air from said plenum chamber flows.
 16. The heating duct as specified in claim 15 wherein the wall is vertical and wherein the air flows up one face thereof and down the other face thereof and exits through said elongated vent. 